The philosophy of create a building to perform a particular function for a time and move on to something else made the 'functional' designs a natural conclusion.

The function of the building dictated the design of the building.

The flow of people within the building, the necessity for light, space and movement determined the best, most efficient design for the building.

Most were rather plain, box-like structures with flat roofs, lots of windows and Spartan esthetics.

They became the symbols of modern 'sweat shop' office space in which people fit into the space much like you would place machines in a factory floor.